1. Field of the Invention
The present invention relates to radar and communication systems. More specifically, the present invention relates to radar and communication systems that are adapted to circumvent interference.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Conventional radar systems transmit and receive at a single carrier frequency. As a result, these systems were susceptible to interference. Many schemes have been developed to address this problem, two of which involve frequency hopping and the use of a spread spectrum. Frequency hopping involves the transmission of a block of data at one carrier frequency, "hopping" to another carrier frequency and transmitting another block of data and so on. Unfortunately, when frequency hopping is employed, it is difficult, if not impossible, to coherently add individual pulses together to improved the signal-to-noise ratio. While slow hopping may preserve the (phase) coherency of the pulses, slow hopping is considerably more susceptible to interference.
This problem is obviated somewhat with spread spectrum transmission. To achieve a spread spectrum with a conventional radar, either multiple receivers must be used or a single receiver may be used where the exact range to the target is known. To determine the range to the target, the single receiver systems are tuned to a single carrier frequency at which several pulses are transmitted and received. Any doppler shift in the received signal is detected and used to provided range and velocity measurements.
Unfortunately, single channel receivers suffer from interference and scintillation. The interference may be due to many sources including spurious radiation from another radar or the accidental operation of another radar at the same frequency. Clearly, such interference can seriously impair the performance of single channel systems.
Scintillation occurs when several returns from a target add destructively. The net result is a fading of the target making it difficult to maintain a track on the target.
Finally, the range measurement may be somewhat ambiguous in that conventional systems can not discriminate between multiples of a given distance.
Thus, there is a need in the art to mitigate interference and scintillation problems in connection with the use of single channel radar systems and to eliminate ambiguity in range measurements.